The present invention relates generally to a control apparatus for fluid fuel burners of the type having an intermittent pilot and a hot surface ignitor, and more particularly to an arrangement of such apparatus in which energization of a fuel valve is conditioned on flow of electric current through the ignitor.
For reasons set forth in detail in a number of prior references, including U.S. Pat. Nos. 5,020,988, 5,035,607 and 5,133,656, a gas burner system employing an intermittently operating pilot ignited by a hot surface ignitor has become a preferred burner system arrangement. One safety concern with such an arrangement is that fuel gas not be supplied to the burner if the ignitor is not operating properly. A variety of approaches have been taken to addressing this concern. For example, in the burner control system of U.S. Pat. No. 5,020,988, fuel valve energization is controlled by a circuit, including a sequencer which locks out energization to a pilot valve, and, in turn, prevents energization of a main valve where attempts to light a pilot burner have been unsuccessful. U.S. Pat. No. 5,035,607 discloses a burner control system in which ignitor voltage and/or current are monitored to indicate operating state of the ignitor, and used to prevent energization of the fuel valve in the event proper ignitor operation is not indicated.
In both of the previously described arrangements, safety is ensured by sensing a condition related to proper ignitor operation, and utilizing the sensed condition to control a fuel valve operator. Each of these arrangements utilizes a flame sensor for detecting presence of a pilot flame, which condition implies proper operation of the ignitor. Detection of a pilot flame also causes power to be cut to the ignitor to prolong ignitor life, and causes opening of a main fuel valve. The arrangement of U.S. Pat. No. 5,035,607 also implies proper operation of the ignitor from sensed voltage and current conditions at the ignitor, and does not allow fuel to be supplied to the pilot or main burners in the absence of predetermined voltage and/or current conditions, which provides additional safety.
A more direct and simple arrangement for preventing supply of fuel to a burner if the ignitor is not operating properly, is to connect the fuel valve solenoid and ignitor in series so that the same current energizes both the ignitor and fuel valve. Thus, any condition which interferes with adequate current through the ignitor, such as the ignitor burning open, also prevents operation of the fuel valve. Such a system is shown in U.S. Pat. No. 5,133,656. However, the arrangement disclosed in this patent is only suitable for a single fuel valve, and not to a dual fuel valve for use in a burner configuration including both pilot and main burners.
The applicants have devised a burner control system which incorporates a safety feature similar to that of U.S. Pat. No. 5,133,656 into a dual fuel valve system, thus providing simplicity and direct fuel valve safety control in an intermittent pilot type of fuel burner.